1. Field of the Invention
The present invention generally relates to variable inductors, and more particularly, the present invention relates to variable inductors for use in mobile communications equipment.
2. Description of the Related Art
In electronic equipment, and in particular, in mobile communications equipment such as cellular telephones and car telephones, which are required to be miniaturized, miniaturization of internal components is also necessary. The higher the operating frequency, the more complex the circuitry must be. Also, there must be minimal variation among components. Referring to FIG. 5, a circuit including a center tap electrode pattern connected to the electrical center point of two coils may be obtained by mounting two coils 21 and 22 on a printed circuit board 26 and then electrically connecting the two coils 21 and 22 via circuit patterns 23 and 24 and a center tap electrode pattern 25 on the printed board 26. The inductance values of the coils 21 and 22 are varied by detaching the coils 21 and 22 and replacing them with two different coils which have different inductance values and which are balanced in advance. Alternatively, variable inductance coils are used for the coils 21 and 22 to vary and balance the inductance values of the two coils 21 and 22.
The above methods fail to balance the inductance values of the coils 21 and 22 due to variations in the inductance values of the coils 21 and 22 and positional deviations of the coils 21 and 22 when they are mounted. This causes the center tap electrode pattern 25 to be connected at a location that is spaced away from the electrical center point of the coil defined by the coils 21 and 22. The coils 21 and 22 are electrically connected through the center tap electrode pattern 25 disposed on the printed board 26, which configuration occupies substantial space on the printed circuit board 26.
The method of replacing the coils 21 and 22 with two different coils to vary the inductance values involves the burdensome and difficult work of dismounting the coils 21 and 22, and hence it is difficult to automate this process. Also, the method of using the variable coils for the coils 21 and 22 involves the burdensome and difficult work of balancing and adjusting the inductance values of the coils 21 and 22, and hence it is difficult to automate this process. The lower the desired inductance value, the more powerful the influence of inductance components of the patterns 23 to 25. Therefore, it is difficult to obtain a minimal inductance value easily and economically, while also obtaining a miniaturized component.
In order to overcome the problems described above, preferred embodiments of the present invention provide a variable inductor including at least two coils which occupy minimal space on a printed circuit board and having inductance values which are easily adjusted to be reliably and uniformly balanced.
According to one preferred embodiment of the present invention, a variable inductor includes an insulating substrate, at least two substantially meandering coils provided on the insulating substrate, a trimming electrode arranged to adjust an inductance value, which is disposed on the insulating substrate outside of the region where the two coils are located and which electrically connects the two coils, two input/output external electrodes electrically connected to one end of each of the two coils, and an intermediate tap electrode electrically connected to another end of each of the two coils.
The trimming electrode is trimmed to vary the inductance value between the input/output external electrodes of each coil, or the inductance value between the input/output electrode and the intermediate tap electrode, without disrupting the balance between the inductance values of the two coils. The trimming electrode is disposed outside of the region where the substantially meandering coils are located, thereby reducing the degree of interruption in which the trimming electrode interrupts a magnetic field generated by the meandering coils. Therefore, an inductor having a greatly increased, very high Q-value is achieved.
The distance between adjoining portions of the coils may be set to be at least about twice the line width of the coils, so that the distance between the magnetic fields generated in the adjoining portions is increased, and magnetic field interference is thereby minimized.
Other elements, features, characteristics and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention which refers to the accompanying drawings.